Solid core golf balls are well known in the art. Typically, the core is made from polybutadiene rubber material, which provides the primary source of resiliency for the golf ball. A known drawback of polybutadiene cores cross-linked with peroxide and/or zinc diacrylate is that this material is adversely affected by absorption of water vapor, which reduces the resiliency of the cores and degrades their properties. Thus, these cores must be covered quickly to maintain optimum ball properties. A cover that protects the core from the elements and repeated impacts from golf clubs is typically made from ionomer resins, balata, and urethane, among other materials, lonomer covers, particularly hard ionomers, offer some protection against the absorption of water vapor. However, it is more difficult to control or impart spin to balls with hard covers. Conventional urethane covers provide better ball control but offer less resistance to water vapor than ionomer covers.
Prolonged exposure to high humidity and elevated temperature may be sufficient to allow water vapor to invade the cores of some commercially available golf balls. For example, at 38° C. and 90% humidity over a sixty day period, significant amounts of moisture enter the cores and reduce the initial velocity of the balls by 1.8 ft/s to 4.0 ft/s or greater. The change in compression may be reduced by 5% or more. The absorbed water vapor also reduces the golf ball coefficient of restitution (“COR”). When a golf ball is subjected to prolonged storage and/or use under ambient conditions such as 25–35% RH, as well as conditions of high temperature and high humidity, the COR of the golf ball tends to decrease over time due to water vapor absorption.
Several prior patents have addressed the water vapor absorption problem. U.S. Pat. No. 5,820,488 discloses a golf ball having a water vapor barrier (“WVB”) layer disposed between a core and a cover. The WVB layer may comprise polyvinylidene chloride (“PVDC”) or vermiculite. It can also be formed by an in situ reaction between a barrier-forming material and the outer surface of the core. U.S. Pat. Nos. 5,885,172 and 6,132,324 disclose, among other things, a golf ball with a polybutadiene or wound core having an ionomer inner cover and a relatively soft outer cover. The hard ionomer inner cover offers some resistance to water vapor absorption, while the soft outer cover provides desirable ball control. U.S. Pat. No. 6,232,389 discloses the application of a dispersed exfoliated layered filler in an elastomeric polymer based barrier coating mixture so as to reduce water vapor permeability in golf balls and other objects by at least 5-fold. Preferable fillers include layered silicates such as bentonite and vermiculite. U.S. Pat. No. 6,287,216 discloses a wounded golf ball having a liquid center surrounded by a thermoplastic core layer formed of a hydrophobic material that has a water vapor permeation rate of less than about 170 g·mil/100 in2·24 h.
Prior art referenced above typically resort to the incorporation of a WVB material in an existing layer or a designated WVB layer to overcome the water vapor absorption problem in golf balls, escalating manufacturing cost and construction complexity. It is therefore desirable to provide cost-effective material compositions that have general characteristics suitable for golf ball constructions with concomitant WVB properties.
One particular class of polymers suitable for golf ball compositions of the present invention is fluoropolymers. Fluoropolymers are well known for their excellent resistance to outdoor weathering and ultraviolet irradiation, high degree of physical toughness, chemical inertness, water and gas impermeability, low moisture absorption, good abrasion resistance, non-tackiness, resistance to soiling, as well as a significant retention of these properties at both low and elevated temperatures. This rare combination is due to the strength of the C—F bond, one of the most stable bonds known. Other desirable properties of the fluoropolymers include high elongation, low coefficient of friction, low wear rate, good resistance to swell in solvents, low refractive index, and low dielectric constant. These desirable properties allow the fluoropolymers to be widely used as self-supporting layers or outer coatings on various substrates.
Disclosures of fluoropolymer applications in golf ball compositions, however, are limited. U.S. Pat. No. 5,962,140 describes a golf ball having a core and/or an intermediate layer comprising a functionalized fluoropolymer wherein the fluoropolymer may be an ionomeric perfluoropolymer that is sulfonated or carboxylated or a derivative thereof U.S. Pat. No. 6,133,389 discloses amorphous tetrafluoroethylene-hexafluoropropylene (“TFE-HFP”) dipolymers, and other copolymers containing TFE, HFP and a third monomer, useful as coatings for golf balls. U.S. Pat. No. 6,217,464 discloses a golf ball having a lubricating material on its surface for reducing the spin imparted by a striking golf club. The lubricating material may be fluoropolymer, and the coating thickness is less than about 0.010 inches.
There remains a need, however, for further development of golf ball compositions comprising fluoropolymers, particularly non-ionomeric fluoropolymers (“NIFP”), in multi-layer golf ball constructions.